Pseudomonas aeruginosa, an opportunistic pathogen, can cause fatal infections in debilitated or immunocompromised patients. Elastase from Pseudomonas is a major virulence factor that can cause lung injury and inflammation. By damaging the epithelium, elastase could increase airway permeability to proteins, extend infection and alter critical defense mechanisms. Influx of neutrophils into the lung could potentiate the injury. This proposal is to study mechanisms of increased epithelial permeability by Pseudomonas elastase (PE) alone and in combination with activated neutrophils. PE administered by aerosol to guinea pigs increases permeability of the pulmonary epithelium, presumably by affecting tight junctions. Neutrophil (PMN) accumulation in response to a chemotactic agent also increases epithelial permeability. It is our hypothesis that both mechanisms contribute to lung injury in bacterial infection. We will use a guinea pig model to (1) establish the role of PMN in PE-induced injury; (2) to determine whether influx of PMN occurs in response to release of IL-8 by PE or other products of Pseudomonas aeruginosa; (3) to establish whether PE-induced injury, alone or in combination with PMN, involves disruption of the zonula occludens or other structures within the junctional complex. Experiments with cultures of guinea pig and rat epithelial cells will relate PE-induced changes in permeability of cell monolayers to alteration of junctional proteins, cytoskeletal elements and extracellular matrix receptors. Cultured cells will be used to determine if PE alone, or in combination with activated PMN, damages junctional proteins and thereby alters transepithelial electrical resistance and permeability to radiolabeled proteins. Other aspects to be explored are: (1) the relation of junctional components to epithelial barrier function; (2) the role of the epithelial cytoskeleton in maintenance of the permeability barrier; (3) the formation and release of PMN activating cytokines (IL-8) by epithelial cells. The in vitro studies will complement those in the intact animal and will aid in defining mechanisms through which PE and other Pseudomonas toxins injure the lung.